Mosquito pupae are aquatic and are buoyed up in the water by a bubble of gas in a cavity (the ventral air space) formed by their developing mouthparts, antennae, legs and wings. During the past two years I have found that the volume of this gas is variable. I am studying the factors which are involved in this variation in volume. I am also studying the mechanism by which the ventral air space is filled, spontaneous variations in buoyancy, diving behavior and the histology and ultrastructure of the ventral air space and first abdominal spiracles. The methods being applied include the following: (1) standard histological techniques; (2) light microscopy; (3) scanning and transmission electron microscopy; (4) microsurgical techniques; and (5) several special techniques which I have devised in order to study pupal buoyancy. BIBLIOGRAPHIC REFERENCE: 1. Romoser, W.S. 1975. Buoyancy and ventilation in Aedes aegypti (L.) pupae (Diptera: Culicidae). J. Med. Ent. 12 (5) :547-550.